In order to improve wear resistance of aluminum alloy，the aluminum alloy was treated by micro-arc oxidation (MAO) in the hexametaphosphate composite electrolyte with adding different contents of graphene oxide (GO) nanoparticles.Scanning electron microscopy(SEM)，X-ray diffractometer (XRD)，film thickness gauge and microhardness tester were used to analyze the effects of GO on the micromorphology，phase composition，element distribution，thickness and microhardness of micro-arc oxide coatings.Furthermore，the friction and wear properties of aluminum alloy micro-arc oxide coatings under different GO concentrations were studied.Results showed that the addition of GO nanoparticles in the electrolyte had a significant effect on the micro-arc oxide coating.The growth rate of Al2O3/GO coatings increased with the increase of GO content，and the main components were α-Al2O3 and γ-Al2O3.With the increase of GO concentration，the microhardness of the micro-arc oxidation coating was significantly improved compared with that of pure 2A12 aluminum alloy.Owing to the incorporation of C elements into the coating interface during the electrolytic oxidation process，the surface of the Al2O3/GO coating became dense and smooth，the friction coefficient was significantly reduced and the wear resistance was raised.In general，this method could provide a new idea for strengthening surface wear resistance of aluminum alloy and has great significance for expanding the application of aluminum alloys.

 As a biomedical material，TC4 titanium alloy is widely used in the field of bone tissue repair in clinical practice，with annual consumption of about one million pieces in China.However，the properties of TC4 titanium alloy as low wear resistance and poor biological activity seriously restricted its expansion in engineering application.Therefore，a micro-arc oxidation/hydrothermal coating on surface of TC4 was fabricated by utilizing the micro-arc oxidation/hydrothermal synthetic composite technology，and the effects of La(NO3)3 doping amount in the hydrothermal synthesis solution on the phase composition，micro morphology，microhardness，wear resistance and other parameters of the micro-arc oxidation/hydrothermal coating on TC4 titanium alloy were surveyed.Moreover，the micro-arc oxidation/hydrothermal coating on TC4 titanium alloy was characterized by XRD，SEM，microhardness tester and friction and wear testing machine.Results showed that the micro-arc oxidation/hydrothermal coating on TC4 titanium alloy was mainly composed of anatase TiO2 and hydroxyapatite.After hydrothermal treatment，La3+ in the synthetic solution entered the composite coating and participated in the coating reaction.With the increase of La(NO3)3 doping amount，the content of hydroxyapatite phase in the composite coating increased first and then decreased.When the doping amount of La(NO3)3 exceeded 24 mmol/L，the coating surface became smoother.In addition，the microhardness of micro-arc oxidation/hydrothermal composite coating on TC4 titanium alloy decreased first and then increased，and the friction coefficient increased first and then decreased.As the doping amount of La(NO3)3 reached 24 mmol/L，microhardness of the composite coating on TC4 titanium alloy acquired the minimum value，and it was about (271.8±3.1)HV9.8 N，the friction coefficient of the composite coating obtained the maximum value，and it was about 0.8～0.9.

In order to improve the wear resistance of 7075 aluminum alloy surface，the hard ceramic coating on the aluminum alloy surface was constructed by micro-arc oxidation technology in the electrolyte solution doped with nano-BN particles.The effects of the addition of nano-BN particles on the arc initiation voltage of the micro-arc oxidation process，surface morphology，porosity，phase composition，thickness，roughness，microhardness and friction and wear properties of coating were investigated by means of scanning electron microscopy (SEM)，energy dispersive spectrometer (EDS)，X-ray diffractometer (XRD)，photoelectron spectrometer (XPS)，roughness tester，microhardness tester，friction and wear testing machine.Results showed that the coatings were mainly composed of α-Al2O3 and γ-Al2O3 phase.Nano-BN particles increased the arc initiation voltage，and increased the thickness，roughness and hardness of coating.When the concentration of nano-BN particles was 0.3 g/L，the overall performance of the as-obtained micro-arc oxidation coating was the best.At this time，the number of micropores in the coating was small，the pore size was small，and the surface density was high.Compared with the coating prepared in the basic electrolyte，the coating’s surface porosity decreased from 6.617%to 3.518%.Meanwhile，the hardness reached the highest value 916.7 HV10 N，the thickness was 20 μm，and the roughness was 2.38 μm.The friction coefficient was reduced to 0.7，and the wear rate decreased to 7.84×10-5 mm3/(N·m).

During the preparation and service process of micro-arc oxidation coatings，phenomena such as uneven growth or surface wear and peeling emerged，so the micro-arc oxidation coatings should be removed to achieve the purpose of secondary preparation and reuse.Aiming at the bottleneck problem of difficulty to remove micro-arc oxidation coating with high bonding strength，a novel plasma electrolytic removal(PER) technique was presented in this work.By comparing and analyzing the coating removal rates at different voltages，thickness change，and microstructure after coating removal at different times，it was found that the coating removal efficiency was the lowest with the applied voltage of 260 V，and the coating was completely removed after 11 min.When the voltage was increased to 320 V，the coating was completely removed in only 6 min.This was due to the large applied voltage，which made it easier to generate multiple and stable plasma discharge channels，thus realizing rapid removal of micro-arc oxidation coating.Furthermore，a synergistic mechanism of peeling，thinning，and dissolution in the removal of coatings by plasma electrolysis was proposed.The PER technique exhibits high efficiency and environmental protection，which has broad application prospects in the fields of aerospace，medical instruments and so on.

In order to improve the high temperature oxidation resistance of TC4 alloy，an anti-oxidation ceramic coating was prepared on the surface of titanium alloy by micro-arc oxidation in the NaAlO2+ Na3PO4 electrolyte system.The phase composition and microstructure of the coating were characterized by XRD，SEM and EDS，respectively.The hardness and elastic modulus of the coating were tested by nano indenter.In addition，the high temperature oxidation resistance and thermal shock resistance of the micro-arc oxidation coating were studied.Results showed that the surface of the micro-arc oxidation coating was porous.The coating was mainly composed of Al2TiO5 and rutile TiO2 phase.The nano hardness of microarc oxidation coating was (7.8 ± 0.6) GPa，significantly higher than that of TC4 alloy [(4.0 ± 0.2) GPa].After cyclic oxidation at 700 ℃for 80 h，the weight gain per unit area of micro-arc oxidation coating was only 0.73 mg/cm2，which was far less than the weight gains of TC4 alloy (20 mg/cm2)，showing good high temperature oxidation resistance.After 25 thermal shocks at 700 ℃，the coating had no scaling，indicating excellent thermal shock resistance.Hence，it could be seen that micro-arc oxidation coating could effectively prevent the diffusion of oxygen，significantly reducing the oxidation rate of titanium alloy and improving the high temperature oxidation resistance of titanium alloy.

In order to improve the wear resistance and high temperature oxidation resistance of TC11 titanium alloy，Nd2O3 particle-doped micro-arc oxidation coatings were prepared by adding different concentrations of Nd2O3 particles.The effect of Nd2O3 concentration on the microstructure and phase composition of micro-arc oxidation coatings on TC11 titanium alloy was studied by scanning electron microscope and X-ray Diffractometer.Meanwhile，the wear resistance and high temperature oxidation resistance of the coating was evaluated.Results showed that after adding Nd2O3 particles，the number of micropores on the surface of the coating decreased，and the coating phase was mainly rutile TiO2 and anatase TiO2.With the increase of Nd2O3 concentration，the content of Nd element in the coating gradually increased，and the coating thickness first increased and then decreased.When the concentration of Nd2O3 was 1 g/L，the comprehensive performance of the prepared micro-arc oxidation coating was the best，which possessed the average thickness of 8.68 μm，the wear loss of 0.43 mg，the wear scar width of 598.04 μm，and the high temperature oxidation weight gain of 0.139 mg/cm2.Compared with the TC11 titanium alloy and the sample without adding Nd2O3 particles，the high temperature oxidation resistance of the micro-arc oxidation coating was significantly improved after adding 1 g/L Nd2O3 particles，and the wear resistance decreased compared with that without adding Nd2O3 particles.